Cracking hydrocarbon oils



Sept. 12, 1944. H. B. coKE 2,358,149

cRAcKING HYDRocARBoN 0111s Filed Dec. 23, 1938 4 sheets-sheet 1\ Sept.l2, 1944.

H. B. COOKE CRACKING HYDROCARBON OILS wfv@ Sept. l2, 1,944. H. B. cooKECRACKING HYDROCARBON OILS Filed Dec. 23, 1958 4 sheets-sheet s Horace.5. O00}%y Sept. l2, l

H. B. coQKE 2,358,149 CRACKING HYDROCARBON `OILS Flednec. 2s, 1958Y 4sheets-sheet 4 Horace@ Cooke, Y'

Patented Sept. 12, 1,944

2,358,149 oRAcKING nYDRocAR'BoN oILs Horace B. Cooke, Alexandria, Va.,assignor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation ofPennsylvania Application December 2.3, 1938, Serial No. 247,504

rc1. 19e-9) '7v Claims.

My invention relates to p1 ocesses for cracking hydrocarbon oils toobtain gasoline hydrocarbons useful as motor fuel and having highanti-knock value when so used. It relates more particularly to improvedmethods of obtaining gasoline hydrocarbons from crude petroleum stocks,wherein such stocks are rst distilled in order to recover a plurality offractions of different boiling-point ranges, these fractions aresegregated and subjected to catalytic cracking and thermal crackingrespectively, and normally gaseous hydrocarbons thereby produced arerecovered and delivered to the thermal cracking operation in order topromote the degree of cracking obtained therein and to effect aconversion of said gaseous hydrocarbons to gasoline-like hydrocarbons ofhigh anti-knock value; all as more fully-set forth and describedhereinbelow in further detail.

Within the past few years great strides have been made in the art ofcracking petroleum oils. These advances, for the most part, derive fromthe ever-increasing incentive to produce a maximum yield of motor fuelof maximum anti-knock value. Those processes which are believed to havemade substantial progress in this direction may in general be dividedinto two categories; first, processes involving conversion orpolymerization of the normally gaseous hydrocarbons produced inoil-cracking operations, and` second, catalytic oil-cracking processes.But while much thought and time has been expended in the development ofthese individual types of processes,

comparatively little thought has been given to methods of combining themin a unitary conversion operation.

A considerable number of separate gas-polymerization processes have beenproposed and some have been operated cna large scale. The opinion isgrowing, however, that such processes are likelyto nd their greatestutility either for the recovery of gasoline-like hydrocarbons fromnatural gases or, as in the case of certain catalytic-typepolymer-ization processes, for the relatively small scale manufacture ofspecial fuels, such as iso-octane, the market for which is stillcomparatively limited. In so far as gases derived from refinery crackingoperations are concerned, it is believed that the greatest advance inthe art has been made inthe development of oilcracking processes of theso-called gas-reversion type, in which normally gaseous hydrocarbons lproducd in cracking the hydrocarbon oil are recirculated to theconversion zone. A process of this character is disclosed in prior U. S.Patents conditions remaining the same.

.highly advantageous results.

Nos. 2,135,014, 42,135,108 and 2,135,109 to Povl Ostergaard. Othersprior to Ostergaard had proposed to recirculate-Ca and C4 hydrocarbonsto the cracking zone of an ordinary oil-cracking operation, but at leastin such cases as involved the return of these gases for reactionpurposes and without the presence of non-reactive or diluent gases, hadconfined themselves to operations conducted under the ordinaryoil-cracking conditions which would have obtained for. the `same oil.Ostergaard increased the degree of conversion per pass and the operatingtemperature in an operation of this kind, above those which wouldnormally obtain and in fact above those which could be maintained underotherwise similar conditions and without carbon deposition, if the sameoil were cracked in the same apparatus without recirculation of thereactive normally gaseous hydrocarbons.

The gas-reversion process has been successfully applied to' a widevariety of cracking stocks, with Strikingly enough, however, it has beenfound that the optimum advantages of the gas-reversion type of systemgenerally are obtained when the process is applied to the cracking orre-forming of naphthas and similar light stocks containing substantialamounts of hydrocarbons within the gasoline boilingpoint range, no doubtpartly because of the high temperatures possible when operating on lightstocks of this character. On the other hand,

this type of process is also especially useful and advantageous inconjunction with the cracking of very heavy or residual stocks, such forexample as reduced crudes. The conversion temperatures employed in suchoperations are, of course, considerably lower than those employed inre-forming or cracking lighter and more refractory stocks, but are4nevertheless considerably higher than would be used if the same heavystock were cracked in the absence of the recirculated normally gaseoushydrocarbons, other I For this reason, the gas-reversion process asapplied to such heavy stocks is highly advantageous, primarily from thestandpoint of the far greater conversion per pass possible with respectto the heavy oil, as distinguished from the conversion per pass of thenormally gaseous. hydrocarbons. Gas conversion is of course eiected, butthe conversion per pass of the normally gaseous hydrocarbons isnaturally lower when cracking a heavy residual stock than when crackingnaphtha or other light stock. This in turn makes it possible to producea far greater amount of gas-oil charging stock suitable for subsequentcracking to gasoline. It is not intended to imply that a gas-reversionprocess is not applicable to the cracking of gas-oil. As a matter offact the process has been successfully applied to the cracking ofgas-oil, and as so applied results in an increase in both the yield andanti-knock quality of the nal gasoline produced as compared with thermalcracking processes in which gas recirculation is not employed. However,the advantages of the process are believed to show up more strongly andits'economies are believed to be most evident, in connection with there-forming of naphthas and light stock, on the one hand, and thecracking'or so-called viscosity-breaking of very heavy stocks, on theother hand.

VA large number of catalytic cracking processes have been proposed,v allcharacterized by the presence of a catalyst of one type or another inthe conversion zone and usually-by the employment of relatively lowpressures. The Houdry process, employing as a typical catalyst anactivated hydrosilicate of alumina or the like, is a process of thistype. On account of the necessary periodic interruption of this type ofprocess, in order to eiect periodic regeneration of the catalystemployed, and for certain other reasons, the pressures employed in thesecatalytic processes are for the most part extremely low, rarely if everexceeding 50 pounds per square inch in the catalyst contact zone. Forthis reason it is somewhat dicult to combine gas recirculation with suchcatalytic cracking operations in an eiilcient and eiective manner.

Moreover, these types of processes in general tend to produce ratherhigh yields of normally gaseous hydrocarbons, as is true of low-pressureoperations generally, and they are for the most part lacking in ultimateeconomyI and advantages witli respect to the cracking or re-forming ofnaphthas and similar light stocks. AThat is especially true in instanceswhere the lead susceptibility of the cracked gasoline product is low, asis usually the case. Moreover, there is considerable difliculty inapplying a catalytic process of this character to the conversion ofheavy residual stocks, which on account of their carbon-formingtendencies 'tend to interfere with the effectiveness of the catalystemployed.

In accordance with my invention, however, it is possible to secure themaximum advantages andeconomies of both types of processes describedhereinabove, together with advantages and economies which could not beobtained with respect to either type of operation considered alone.

Myinvention contemplates the separation, by distillation, of a crudepetroleum into a plurality of fractions of ldifferent boiling-pointranges, including a naphtha fraction suitable for reforming to highanti-knock gasoline motor fuel, and at least one heavier fraction. Thenaphtha thus recovered is re-formedin a gas-reversion type operation@preferably of the Ostergaard type) in which the naphtha is 'subjectedto thermal conversion in the presence of recirculated normally gaseoushydrocarbons containing 3 to 4 carbon atoms per molecule, a considerableportion of which are produced in the re-.forming operation itself. Aheavier fraction recovered from the distillation of the original crudeis subjected to separate catalytic cracking, ordinarily at lowpressures, and normally gaseous hydrocarbons containing 3 tov 4 carbonatoms permolecule produced in this operation are deversion units.

livered to the naphtha re-forming operation referred to hereinabove.

As will be shown hereinbelow, the heavy fraction thus subjected tocatalytic cracking may comprise a reduced or topped crude, or it maycomprise a virgin gas-oil fraction. In the latter event, the residualreduced crude is, in accordance with some embodiments of my invention,subjected to cracking in the presence o recirculated C3 and C4hydrocarbons in the manner generally similar to that employed withrespect to the naphtha re-forming operation reierred to hereinabove. Inone embodiment of my invention described hereinbelow,'such a reducedcrude fraction is subjected' toA a viscosity-breaking or mild crackingoperation conducted in the presence of Ca and C4 hydrocarbons and thevaporous products of conversion in this operation are returned to thecrude distilling operation in such a, manner that the gas-oil produced jin this conversion-stage is commingled with the gas-oil derived directlyfrom the crude, and subsequently delivered to the catalytic crackingzone.

The segregation of the C3 and C4 hydrocarbons produced in the severalcracking operations may be variously accomplished but in the main iseffected by subjecting the fractionated gasoline-free products ofconversion to scrubbing with the naphtha fraction about to bedeliveredinto the thermal conversion zone. In some instances gas-oilcondensate may also be withdrawn at one or more points in the system,cooled, and employed as an absorbent for the recovery of C3 and C4hydrocarbons from one or more of the cracking operations. When this isdone, it is usually desirable to employ the thereby enriched gas-oil asa quenching and cooling medium in one or more of the thermal con- Inorder to lighten the load on the nal absorber and in order to provideadditional iiexibility, a pressure condensation step may be providedahead of the absorber in order` to recover a liquefied propane-butanefraction, which is then returned to one or more of the conversion zonesin admixture with the oil traversing the same. These and yothermodifications will be described more fully hereinbelow.

i My invention also contemplates such additlonal operating details andmodifications, and such additional operative advantages and economies,as will hereinafter be found to obtain.

In order that my invention may be fully set forth and understood, I nowdescribe, with reference to the drawings accompanying and formmg a partof this specification, a number of forms and manners in which myinvention may be practiced and embodied. In these drawings Figuresl 1,2, 3 and 4 are more or less diagramtemperatures in various portions ofthe unit and the like, the application of which will be obvious to thoseskilled in the art.

Similar reference numerals designate similar parts in the several viewsof the drawings,

In the embodiment illustrated in Fig. 1, a crude petroleum chargingstock is introduced into the i system through pipe I by means of a pump2 and is preheated in a suitable manner, as for example by means of aheated pipe coil 3 located within a furnace 4, to a suitable distillingtemperature, usually a temperature at which no substantial cracking iseffected. Such preheating temperatures will be of the order of 700 to150 F. It will be understood that the preheating may be accomplished invarious manners, as for example by heat exchange in other portions ofthe system to be described hereinbelow, and that the same considerationswill apply to many instances in which heating and cooling operations areinvolved.

The preheated crude then passes through a line 5 having a valve 6 into adistilling column or flash tower 1 of more or less conventional design.This column is provided with suitable cooling or reuxlng means such as acoil 8, with suitable gasand-liquid-contact devices such as bell trays 9and with one or more naphtha trap-out trays I0. By reason of the heatimparted to the crude oil and the low or atmospheric pressure maintainedin the column 1, distillation takes place and a considerable portion ofthe crude oil is distilled. The light products, including any fixedgases which may be present and light virgin gasoline, are withdrawn from.the head of the column throughv a line l2 to a condenser I3 and aseparator I4 from which the xed gases and the light virgin gasoline areremoved through lines l5 and i6, respectively. Heavy virgin naphthasuitable for re-forming is withdrawn as a side stream from the trap-outtrayy i0 and passes through a line l1 to a cooler l8. As will beunderstood by those skilled in the art, the cooler1 I8 and all othercoolers and condensers subsequently shown are water-cooled devices ofmore or less conventional type, effective to reduce the temperature ofthe vapors or oil passing therethrough to approximately atmospherictemperature or a little above. However, it will be understood that moredrastic cooling may be applied wherever necessary or desirable.

If desired, various cuts may be withdrawn as side streams from the tower1 in addition to the naphtha cut withdrawn from the trap-out tray I0.Thus kerosene, gasoline and gas-oil cuts may be so withdrawn. In theinstance shown, however, all ,of the crude oil constituents notvaporized and removed through the line l2 or removed as a side streamfrom the trap-out tray l0 are retained in the reduced or topped crude,which is eventually withdrawn from the bottom of the tower 1 through aline 20.,

The reduced crude fraction so withdrawn is then delivered by means of apump 2l to suitable heating means, such as a still or pipe coil 22located within a furnace 23, and in passing through the coil 22 isheated to a temperature suiiicient to promote conversion in the presenceof the catalyst with which the oil or a portion thereof is subsequentlyto be brought into contact. In the instances shown, in which thecracking of this stock is effected in accordance with the sc-calledHoudry process, the reduced crude ordinarily emerges from the pipe '22at a temperature somewhere around 880 F. or at any rate at suchtemperature as will be sucient to effect vaporization of all but thevery heaviest constituents thereof, and at this temperature passesthrough a valved line 24v into a vaporizer 25. Tar is withdrawn from thevaporizer 25 through a valved line 26 while the vapors pass through avalved manifold vapor line 21 into one of a plurality of catalyst cases28. These catalyst cases are provided with inlet and outlet manifoldconnections as shown in such a manner that they may be alternated asdesired, so that regeneration of the catalyst in one or more of thecases may be effected while the catalyst in another case is on stream.

While I do not wish to limit myself to any particular catalyst or anyspecic conditions of temperature and pressure, it may be stated that asuitable catalyst used in the Houdry'process comprises an activatedhydrosilicate of alumina and that typical conditions of temperature andpressure at this point are from 800 to 900' F. and from atmospheric to20 pounds per square inch gauge pressure. Various modifications of theHoudry process are, however, disclosed in an article entitled Catalyticprocessing by the Houdry process, found at l'page R-5'10 of the NationalPetroleum News for November 30, 1938, and in the patents listed in thatarticle, while various other catalytic cracking processes are describedin prior patents and in the literature,

Under the influence of the catalyst and the heat applied to the oil,conversion takes place resulting in the formation of gasoline and otheruseful hydrocarbons. The converted vapors leave the on-stream catalystcase 28 through a manifold line 29 and enter a fractionating column 30which, as shown, may be of more or less conven. tional design and whichis operated to condense and recover constituents having boiling pointshigher than those desired in the nal gasoline fraction. The gas-oilcondensate thus obtained is removed from the bottom of the column 30through a line 3l, while the gasoline and lighter vapors pass through aline 33 to a condenser 34,

and thence through a line 35 into a separator 35. Condensed gasolinev iswithdrawn from the separator 36 through a valved line 31, while thegases and vapors remaining uncondensed pass through a line 38 into anabsorber 39. A pump or compressor 40 may be provided in the line 38 forthe purpose of maintaining elevated pressures, for example pressures ofor 200 pounds per square inch gauge, in the absorber 39 wherever thisproves desirable for the purpose of promoting efciency of absorption.

In the instance shown, I provide for the recovery of C3 and C4hydrocarbons from the gases entering the absorber 39 through theintroduction to the absorber of a portion of the naphtha recovered inthe crude flash tower 1. The naphtha so recovered, after leaving thecooler I8, passes through a line 42 having a pump 43 and communicatingwith a valved branch line 134 leading into the top of the absorber 39.The gases from the catalytic operation, entering the absorber 39, flowcountercurrent to a stream of cool naphtha thus introduced, and theconditions within the absorber are so regulated. in accordance with theamount and character -of the gases introduced as to effect an absorptionof the C3 and C4 hydrocarbons, or any desired portion thereof, from thegases. The residual gases, comprising for the most part C3 and lighterhydrocarbons, leave the top of the absorber through a valved outlet line45.

The enriched naphtha leaving the absorber 39 and containing C3 and C4hydrocarbons removed by absorption in the absorber 39, then passesthrough a line 46 to a pump 41 which in turn delivers it through a line48 into an elongated pipe coil 49 of restricted cross-sectional areacondenser and rectifier '60.

the naphtha is subjected to thermal conversion at an elevatedtemperature in the presence' of the C3 and C4 hydrocarbons. Substantialconversion is obtained at various temperatures and pressures, rangingfor example from about 950 to 1400c F. and from about 100 to 2000 poundsper square inch gauge pressure, but the best results are obtained whenthe operation is conducted in the manner set forth and claimed in U. S.Patent No. 2,135,014 to Povl Ostergaard. That is to say, the admixtureof oil and normally gaseous hydrocarbons is subjected to a high crackingtemperature substantially in excess of the maximum temperature to whichthe oil alone could be subjected in identical apparatus and underotherwise identical conditions of y conversion without such excessivedeposition of carbon as to prevent continuous operation of the unit forextended periods of time, and ordinarily ranging from about 25 to 300higher than the aforesaid maximum temperature.

During the passage of the oil and normally gaseous hydrocarbons throughthe coil 49 conversion takes place and the heated products are thendischarged through a vapor-transfer line 52 having a pressure-reducingvalve 53 into a tar separator 54. Under the influence of the pressurereduction and cooling, supplied as will hereinafter be shown, vaporseparation takes place, tar being withdrawn from the bottom of theseparator 54 through a valved line 55. The separated vapors are thenpassed through a line 56 into a fractionating column 51 which, as shown,may be of more or less conventional design.

In the fractionating column51, sulicient cooling is effected to causethe condensation of constituents heavier than are desired to be retainedin the final gasoline condensate. These condensed constituents, whichmay be referred to as gas oil, are withdrawn from the bottom of thefractionating column 51 through a line 58. All or a portion of the gasoil thus withdrawn is then delivered by means of a pump 59 to a cooler60 and thence in part through a valved quenching line 62 to thevapor-transfer line 52, and in part through a valved reflux line 63 intothe tar separator 54.

The uncondensed vapors leaving the top of the column 51 pass through aline 65 into a gasoline paratus may be used at this point florcondensing and stabilizing the gasoline produced in the system, such,for example, as that shown and claimed in U. S. Patent No. 2,134,816 toPovl.

Ostergaard. In the instance shown, however, I have for simplicitys sakeshown a conventional rectifying column provided with suitable plates ortrays 61, cooling means 68 located in the head of the column and heatingmeans 69 located in the foot of the column. The heat supplied to theheating coil 69 may be obtained from hot oil produced elsewhere in thesystem, as for example by causing all or a portion of the gas-oilcondensate to traverse this coil. In any event, however, rectificationtakes place in the column 66 with the result that stabilized gasolinecondensate is withdrawn from the bottom thereof through a valved line 1|while the remaining gases pass overhead through a line 12 leading to acondenser 13 and a separator or accumulator 14.

By virtue of the pressures maintained in this portion of the system, andwhich will ordinarily run from 100 to 300 pounds per square inch, aportion of the C3 and C4 constituents present in Various types of aIJ-`'located within a heating furnace 50, and wherein the gases are causedto be condensed in the condenser 13 and collect in the accumulator 14in.

liquefied form. Operation of the cooler 13 at temperatures somewhatbelow atmospheric may be resorted to in order to condense any desiredportion of the Ca and C4 hydrocarbons at this point.

The condensate thereby obtained, comprising liquid butane and propanetogether with their unsaturated analogues, isremoved from theaccumulator 14 through a line 15. 'I'he line 15 is in communication withthe inlet to coil 49 through a branch line 16 having a pump 11 and avalve 18, and with the inlet to the pipe coil 22 of the catalyticcracking unit through a branch line 18 having a valve 80. This apparatusmakes it possible to deliver any desired portion or all of the liquidcondensate from the accumulator 14 either to the coil 49 or to the coil22, or to distribute the liquid condensate to the two coils mentioned inany desired proportion.

The gas and vapors remaining uncondensed in the condenser 13 leave theaccumulator 14 through a line 82 and enter the bottom of an absorber 83.That portion of the virgin naphtha removed in the tower 1 and not usedin the absorber 39 is delivered to the upper portion o1' the absorber 83through a valved line 84 and in passing downwardly through the absorber83 effects a removal, by absorption, of C3 and C4 hydrocarbons'presentin the'gas traversing the absorber. The gases remaining uncondensed, andcomprising for the most part C3 and lighter hydrocarbons, are removedfrom the top of the absorber 83 through a valved exit line 85, while theenriched naphtha reaching the bottoml of the tower 83 is withdrawnthrough a line 86 having a pump 81 and communicating with the line 48.This enriched naphtha is delivered to the pipe coil 49 located withinthe furnace 50 and is there subjected to thermal conversion along withthe enriched naphtha from the absorber 38.

The system illustrated in Fig. 2 is generally similar to thatillustrated in Fig. 1 and described hereinabove with the exception thatprovision is made for effecting absorption of C3 and C4 hydrocarbons inthe absorbers 39 and 83 in a different manner or manners. In someinstances, it may be desirable to use all of the virgin naphtha removedfrom the ash tower 1 as the scrubbing medium in the absorber 83, or inthe absorber 39, and in such instance it is, of course, necessary toprovide a suitable `absorbent for use in whichever one of the twoabsorbers 39 and 83 is not Supplied with this naphtha. As shown in Fig.2, gas oil condensate removed from the bottom of the fractionatingcolumn 51 is delivered after the cooling either to the absorber 39 or tothe absorber 83.' After absorption, the enriched gas-oil is thenreturned to the thermal cracking unit at a point subsequent to theconversion zone. *Referring to Fig. 2 in greater detail, gas oilcondensed in the fractionating column 51 is withdrawn therefrom througha line |00 and is delivered by means of a pump |0| and aline |02 to acooler |03 and thence through a. line |04 which is in communication withbranch lines |05 and |06, having valves |01 and |08 and leadj ing to thetops 'of the absorbers 83 and 39, respectively. Enriched oil from thebottom of the absorber 83 is removed therefrom by a line ||0 having apump and may be delivered either through a valved branch line I2 intothe line 48 and thence into the pipe coil 49, or through a valved branchline ||3 and a line ||4 into the valved conduits 62 and 63 and thenceinto the transfer line 52 and the tar separator 54 in any desiredproportions. Similarly, enriched oil withdrawn from the absorber 39 iswithdrawn therefrom through a line H having a pump H6 and this oil maybe delivered either through a valved branch line H1 into the line 48andthe pipe coil 49, or through a valved branch line ||8 and the linesH4, 62 and 63 into the transfer line 52 and the tar separator 54. y

In the preferred instance, all of the naphtha withdrawn from thetrap-out tray |0 of the tower 1 passes through the lines 42 and 84 intothe absorber 83 and after passing through the absorber 83 the therebyenriched oil is delivered through the lines H0, H2 and 48 to the pipecoil 49. Gas oil withdrawn from the fractionating column 51, or anydesired portionthereof, is delivered through the lines |00, |02, |04 and|06 into the absorber 39 and the enriched oil after absorption of C3 andC4 hydrocarbons in the .absorber 39 is then returned through lines H5,H8, H4, 62 and 63 into the transferline 52 of the tar separator 54. TheC3 and C4 hydrocarbons thus absorbed in the absorber 39 are not in thisinstance delivered directly to the pipe coil 49, but are eventuallypicked 'up in the absorber 83 in the naphtha used therein and then passto the pipe coil 49. This system has the advantage that it increases theconcentration of C: and Crhydrocarbons in the fractionating system ofthe thermal cracking unit and hence the eilciency of condensation andabsorption of these constituents in that unit.

Alternatively, all of the naphtha removed from the crude ash tower 1 maybe passed through the absorber 39, the enriched naphtha then passingthrough lines H5, ||1 and 48 to the pipe coil 49. In this instance,gas-oil withdrawn from the base ofthe fractionating column 51 isdelivered through lines |00, |02, |04 and |05 into the ab sorber 83 andthe enriched gas-oil is then returned through lines H0, H3, H4. 62 and63 into the transfer line 53 (as a quenching medium) and the tarseparator 54 (as a reuxing medium).

In the system illustrated in Fig. 3, provision is made for subjecting alight cut, such as virgin naphtha, and a heavy cut, such as reducedcrude, to separate thermal conversion with gas recirculation, and forsubjecting an intermediate or gas-oil fraction also recovered in thedistillation of the crude to catalytic cracking. The gases in thecatalytic cracking unit are combined with the gases' from the thermalcracking units for recirculation into the latter. made for deliveringgas-oil condensate from the thermal cracking unit into the catalyticcracking unit for conversion.

Referring to Fig. 3 in greater detail, one or more trap-out trays |30are provided lin the crude ash tower 1 at apoint located below thenaphtha trap-out tray |0,.and more specifically at such a point as willenable the withdrawal therefrom of avirgin gas-oil-fraction. The gasoilfraction thus withdrawn is delivered through a pipe |3| andv a pump |32to the pipe coil 22 of the catalytic conversion unit, and thnce directlythrough the valved manifold line 21 to one of the catalyst cases 28. Avaporizer, similar to the vaporizer shown in Fig. 2 may be provided, butwill ordinarily be unnecessary .when cracking such a non-residual stock.Heavy reduced crude unvaporized in the flash tower 1 is withdrawnltherethrough through a line |33 having a. pump |34 and is delivered toa pipe coil |35 located Provision is also y within a heating furnace|36. Before being passed through the coil |35, however, this reducedcrude is joined by propane-lbutane condensaterecovered in the separator14, vand which in this instance. is withdrawn from the separator 14through a valved line |40 and delivered by means of a pump |4| and aline |42 into the line The temperatures and pressures employed in thecoil |35 will, of course, be lower than those employed in the coil 49,which in this instance receives enriched naphtha from the absorber 83.Typical operating temperatures and pressures will run from 850 to 1000F. and from 100 to 2000 pounds per square inch. In any event, how-vever, the best results are secured, as in the coil 49, by operating inthe manner disclosed and claimed in U. S. Patent No.A 2,135,014 to PovlOstergaard and as referred to hereinabove, keeping in mind the characterof each individualv charging stock.

The hot products of conversion leaving the coil |35 are dischargedthrough a, transfer line |31 into the transfer line 52, where theymingle with the products of conversion of thecoil 49 and then pass intothe tar separator 54 and subsequent' Gases remaining uncon-Afractionating units. densed in the accumulator 14 are delivered to theabsorber 83 Where they are scrubbed with virgin naphtha recovered in thecrude flash tower 1. The enriched naphtha, containing C3 and C4constituents recovered from the gases in the absorber .83, is'thendelivered through the line 86, the pump 81 and the line 48 into the pipecoil 49. In the instance shown, the gases remaining uncondensed in theseparator 36 of the catalytic cracking unitare passed through a line |43to a pump or compressor |44 where/they are raised to a pressure equal tothat obtaining in absorber 83 and then pass through a line |45 into thebottom of the absorber 83. Gas-cil condensate recovered in thefractionating column 51 is withdrawn therefrom through a line and passesthrough a pump |5| to a cooler |52. One portion of this cooled gas oilmay be delivered through a valved Vline |53 into the tar separator 54,another portion through a valved quenching line |54 into the transferline 52, and a third portion through a valved quenching line |55 intothe transfer line |31, while any remaining gas-oil from this source maybe delivered through a valved line |56 into the line |3| where it joinsvirgin gas-oil withdrawn from the tower 1 and enters the pipe coil 22 ofthe catalytic conversion unit.

In the apparatus just described in connection with Fig. 3, thefractionated products leaving the heavy oil conversion coil |35 arecombined with and fractionated with the products leaving the re-formingcoil 49. In the system illustrated in Fig. 4, however, the cracking orviscosity breaking of the heavy oil is accomplished in conjunction Withthe crude flash tower, and the products from the heavy-#oil conversionor viscositybreaking coil are fractionated in the crude ash tower alongwith the crude undergoing fractionation.

Referring to Fig. 4 in greater detail, a reduced crude fraction iswithdrawn from the tower 1, which in this instance serves as afractionating tower for the combined products of crude distillation andviscosity-breaking, by means ota trap-out tray 200 located at a pointbelow the point of entry of the preheated crude. This reduced crudefractionis deliveredlby. I neans of j a line20| and a pump 202 to a pipecoil 203 loy cated within a furnace 204. Butane-containing condensaterecovered in the accumulator 14 of the thermal re-forming unit is inthis instance withdrawn by a line 205 and delivered by means of.a pump206 and a line 201 to the line thereby causing this liqueed gas fractionto be commingled with the reduced crude withdrawn from the trap-out tray200 before the latter passes to the conversion coil 203. The conversionoperation conducted in the coil 203 isessentially similar to thatdescribed hereinabove in connection with the operation of the coil ofthe system shown in Fig.` 3. In this instance, however, the productsleaving the coil 203 pass through a transfer line 2I0 having apressurereducing valve 2| I into the lower part of the flash tower 1..Residue or tar separating in the bottom of the ash tower 1 is withdrawnby a line 2I2, while the flashed vapors pass upward through the tower 1and are fractionated therein.

It will be obvious that in this system the fraction withdrawn fromthe'trap-out tray |30 of the tower 1 comprises both virgin gas-oilconstituents and gas-oil constituents produced by the mild crackingeffect in the coil 203. This fraction passes through the line |3I intothe pipe coil 22 of the catalytic conversion unit, as in the systemillustrated in Fig. 3.

As in that system, virgin naphtha recovered from the flash tower 1 isdelivered by means of the line I1, the pump 43 and the line 42 into theabsorber 83 of the thermal cracking unit, and the enriched naphthaleaving the bottom of the absorber 83 is delivered through the lines 86and into the re-forming coil 49.

In this system, inasmuch as normally gaseous hydrocarbons are deliveredto the viscositybreaking or mild cracking operation conducted in thecoil 203, considerable quantities of Cs and C4 hydrocarbons are presentin the overhead products from the tower 1. I have illustrated in Fig. 4means whereby these may be recovered. As shown, gases leaving theseparator I4 through the line I5 arepicked up by a pump or compressor2|9, where they are raised to a pressure equal to that obtaining inabsorber 83, and the compressed gases are then delivered into the bottomof the absorber 83 through a line 220 provided for that purpose.

I have also illustrated in Fig. 4 a procedure absorber 83 sometimescontain substantial quantities of C3 and higher boiling constituentswhich it may be desired torecover for use and ultimate conversion in thesystem. To that end, the gases leaving the top of the absorber 83 aredelivered through a line 22| to a second absorber 222. Gas oil recoveredin the fractionating column 51, or any desired portion thereof, iswithdrawn therefrom through a valved line 223, wherein are located'apump 224 and a cooler 225, and passes to the upper part of the absorber222. In passing down through the absorber 222, the gas oil thusintroduced absorbs Ca and C4 hydrocarbons as well as any heavierconstituents which may be contained in the gases entering the absorber.The enriched gas oil leaving the bottom of the absorber 222 is deliveredthrough a line 230 having a pump 23| into the lines 62 and 63 leading-t0 the transfer line 52 and the tar separator 54, respectively. In thiscase, as in al1 other instances in which oil is delivered to one of thetransfer lines leading from one of the conversion zones, the purpose inthus introducing oil is to arrest and control the reactions initiated inthe respective conversion zone.

Gases remaining uncondensed in the absorber 222 are removed through avalved exit line 232 s and pass out of the system,

With reference to all of the systems shown in Figs. 1 to 4 hereinabove,any gas-oil constituents recovered in the fractionating column 30 of thecatalytic conversion unit may be recycled to the catalytic conversionunit or cracked in a separate coil, with or without a catalyst, and theproducts of cracking may be fractionated along with other products ofconversion, in a marmer which will be evident to any one skilled in theart from the foregoing. However, for purposes of simplicity, I haveomitted the details of such operation from the drawings.

Moreover, the various gasolines recovered in the systems illustrated anddescribed hereinabove, for example at I6, 31 and 1|, may be combined andblended in any desired proportions to produce the final motor-fuelproduct, or they may be used separately. Moreover, these gasolines maybe blended with additional agents for use, as forv example, with theusua1 anti-knock agents, such as tetraethyl lead and the like.

In this case it may be noted that in general the lead susceptibility ofcatalytically cracked gasolines does not usually compare with the leadsusceptibility of thermally cracked gasolines such as those produced inthe thermal cracking zones of the systems illustrated. hereinabove. Thisfact constitutes one of the reasons why, as I have stated, there-forming of straight run gasoline is best carried out in a thermalconversion zone of the. type indicated hereinabove rather than in acatalytic cracking zone.. 4For this reason, the overall anti-knock valueand lead susceptibility of the products obtained in accordance with myinvention represent a distinct improvement over prior art processes.

In referring to catalytic cracking processes I 'have in mind in generalthose processes, usually carried out at pressures of less than poundsper square inch at elevated temperatures ranging from 700 to 1100o F.,wherein a catalyst of some sort or another is employed to promoteconversion reactions tending to form gasoline-like hydrocarbons. I havereferred principally here.. inabove to the Houdry process, but it willbe understood that other types of catalytic processes and othercatalysts may be employed in those instances where catalytic cracking-isindicated. Such catalytic cracking processesA are numerous and wellknown in the art and need not be catalogued here in full. However, byway of exemplication, it may be stated that among the catalysts whichhave been proposed for use in processes of this character and Which tothe extent that they are individually useful and advantageous may beemployed in the catalytic cracking zones of the processes describedhereinabove, are the following: nickel and compounds thereof, such asnickeloxide; chromium and compounds thereof, such as chromlc oxide;compounds of nickel and chromium, such as nickel chromate; phosphoruscompounds, especially metaphosphates, including those of chromium anduranium; aluminas; adsorbent clays; floridin; bauxite; molybdenum sulde;and a wide variety of other compounds, particularlycompounds of metalsand alkaline earth metals.

others alkylation'reactions, but for the purposesof the presentinvention, all of these may be j considered to come under the generalcategory of catalytic cracking catalysts. Most of these catalysts arepreferably employed at low pressures, with regeneration at periodicintervals, but my invention, in so far as it deals withl catalyticcracking, is not so limited.

In referring to normally gaseous hydrocarbons .having 3 to 4 carbonatoms permolecule, I mean propane, propylene, butanes and butylenes, allof which are normally gaseous in a'pure state under atmospheric pressureand temperature conditions. It will be understood, however, that theseconstituents may or may not exist in gaseous form at different points inthe systems illustrated. and consequently the expression referred to isnot intended to imply that these constituents are actually present asgases, for at many points they will exist in the liquid form, by virtueof the pressures employed or because of the presence of liquid oils inwhich they are absorbed, or both.

While I have described and illustrated my invention hereinabove withrespect to numerous operating examples and specific operating details,it is not my intention to limit my invention in its broadest aspect tosuch details or exemplications. My invention may 4be variously practicedand embodied Within the scope of the claims hereinafter made.

What I claim is: y

l. The process of producing gasoline motor fuel of high anti-knock valuefrom a crude petroleum, which comprises: fractionally distilling a,crude petroleum to recover a naphtha fraction and a higher-boilingfraction; subjecting said higher-boiling fraction to conversion at arelatively low pressure in the presence of a catalyst effective topromote pyrolysis reactions,. and fractionating the resultant productsof conversion to recover gasoline and heavier constituents, including agas-oil fraction, therefrom; subjecting said naphtha fraction to thermalconversion at a high cracking temperature and under a relatively highsuper-atmospheric pressure. effective to cause the formation ofgasoline-like products having an increased anti-knock value, andseparately fractionating the `resultant products of conversion torecover gasoline and heavier constituents, including a gas-oil fraction,therefrom; recovering normally gaseous hydrocarbons having 3 to 4 carbonatoms per molecule from the thereby fraction- `ated products ofconversion of one of the conversion operations referred toabove byabsorption in said naphtha fraction, prior to conversion thereof asaforesaid; delivering the thereby enriched naphtha fraction containinggaseous hydrocarbons to the thermal conversion operation for conversionas aforesaid; recovering normally gaseous hydrocarbons having 3 to 4carbon atoms per molecule from the products of conversion of the otheroperation referred to above, by absorption in a gas-oil fractionrecovered as aforesaid; and delivering the thereby enriched gas-oilconstituents to the hot products of conversion in the thermal conversionoperation, as a cooling medium.

2. The process of producing gasoline motor.

troleum, which comprises: fractionally distilling a crude petroleum torecover a naphtha fraction and a higher-boiling fraction; subjectingsaid higher-boiling fraction to conversion at -a relatively low pressurein the presence of a catalyst effective to promote pyrolysis reactions,and fractionating the resultant products of conversion to recovergasoline and heav1er constituents therefrom; subjecting said naphthafraction to'thermal conversion at a high cracking temperature and undera relatively high superatmospheric pressure, effective to cause th'eformation of gasoline-like products having an increased anti-knockvalue, and separatelyfractonating tite resultant products of conversionto 'recover gasoline and heavier constituents, including a gas-oilfraction, therefrom; recovering normally gaseous hydrocarbons having 3to 4 carbon atoms per molecule from the thereby fractionated products ofconversion of the thermal conversion operation referred to above byabsorption in said naphtha fraction before conversion thereof asaforesaid; 'delivering the thereby enriched naphtha containing saidnormally gaseous hydrocarbons to the thermal conversion operation forconversion as aforesaid; recovering normally gaseous hydrocarbons fromthe fractionated products of conversion in the catalytic crackingoperation by absorption in said, gas-oil fraction; and delivering thethereby enriched gas-oil fraction to the hot products of conversion inthe thermal cracking operation, as a cooling medium.

3. The process of producing gasoline motor fuel of high anti-knock valuefrom a crude petroleum, which comprises: fractionally distilling a.crude petroleum to recover a naphtha fraction and a higher-boilingfraction; subjecting said higher-boiling fraction to conversion at arelalively low pressure in the presence of a catalyst effective topromote pyrolysis reactions, and fractionating the resultant products ofconversion to recover gasoline and heavier constituents, including agas-oil fraction, therefrom; subjecting ,said `naphtha fraction tothermal conversion at a high cracking temperature and under a relativelyhigh super-at-j mospheric pressure, effective to cause the formation ofgasoline-like products having an increased anti-knock value` anzlseparately fractionating the resultant products of conversion to recovergasoline and heaver constituents, including a gas-oil fraction,therefrom; recovering normally gaseous hydrocarbons having 3 to 4 carbonatoms per molecule from the thereby fractionated products of conversionof the catalytic conversion operation by absorption in said naphthafraction prior to conversion thereof; deliverngthe thereby enrichednaphtha fraction containing said normally gaseous hydrocarbons to thethermal conversion operation for conversion as aforesaid; recoveringnormally gaseous hydrocarbons having 3 to 4 carbon atoms per moleculefrom the fractionated products of conversion in the thermal crackingoperation l"by absorption in a gas-oil fraction produced as aforesaid;and recycling the thereby enriched gas-oil fraction' into the thermalconversion operation.

4. The process of producing gasoline motor fuel of highganti-knock valuefrom a crude petroleum which comprises fractionally distilling a crudepetroleum to recover a naphtha fraction, a gas-oil fraction and aresidual fraction; subjecting said residual fraction to thermalconstituents therefrom;

version at a mild cracking temperature and under superatmosphericpressure; separating tarry constituents from the products of conversiontherebyobtained and commingling the separated hot products of conversionthereby obtained with the crude petroleum undergoing fractionation;subjecting said gas-oil fraction to conversion at a relatively lowpressure in the presence of a catalyst capable of promoting pyrolysisreactions, and separately fractionating the resultant products ofconversion to obtain gasoline and heavier constituents therefrom;subjecting said naphtha fraction to thermal conversion at a highcracking temperature and under a relatively high superatmosphericpressure, effective to cause the formation of gasoline-like productshaving an increased antiknock value, and fractionating the resultantproducts of conversion to. recover gasoline andheavier constituentstherefrom; recovering normally gaseous hydrocarbons having 3 to 4 carbonatoms per molecule from the gaseous products leaving the crudefractionating operation, the catalytic conversion operation and thenaphtha re-forming operationreferred to above; and subjecting saidnormally gaseous hydrocarbons to conversion in admixture: with theresidual fraction and the naphtha fraction subjected to conversion asaforesaid, respectively.

5. 'I'he process of producing gasoline motor fuel of high anti-knockvalue from a crude petroleum which comprises fractionally dis'tillingacrude petroleum to recover a naphtha fraction, a gasoil fraction and aresidual fraction; subjecting said residual fraction tothermalconversion at a mild cracking temperature and undersuperatmospheric pressure; separating tarry constituents from theproducts of conversion thereby obtained and commingling the separatedhot products of conversion thereby obtained with the crude petroleumundergoing fractionation; subjecting said gas-oil fraction to conversionat a relatively lcw pressure in the presence of a catalyst capable ofpromoting pyrolysis reactions, and separately fractionating theresultant products of conversion to obtain gasoline and heavierconsubjectjng said naphtha fraction to thermal conversion` at a highcracking temperature and under a relatively high superatmosphericpressure, effective to cause the formation -of gasoline-like productshaving an increased anti-knock value, andl fractionating the resultantproducts of conversion to recover gasoline and heavier constituentstherefrom; recovering normally gaseous hydrocarbons having 3 to 4 carbonatoms per molecule from the fractionated gasoline-free products of thenaphtha re-forming operation referred to above; subjecting said normallygaseous hydrocarbons to con- Version in admixture with said residualfraction subjected to conversion as aforesaid; combining the remaininggaseous products from the naphtha re-forming operation with thefractionated gaseous products 'from the catalytic cracking operation;scrubbing the thus combined products' gas-oil is'4 recovered byfractionation of the products of conversion of the naphtha re-formingoperation, the combined gaseous products after being scrubbed with saidnaphtha fraction as set forth in claim 18 are scrubbed with said gas-oilfraction, and the thereby enriched gas-oil fraction is introduced intothe hot .products of conversion leaving the naphtha conversion zone, asa cooling medium.

'7. The process ,of producingl gasoline motor fuel cf high anti-knockvalue from a crude re,- troleum which comprises fractionally distillinga crude petroleum to recover a virgin naphtha fraction, Virgin gas-oilconstituents and a residual fraction; subjecting said residual fractie.Ato thermal conversion at a mild cracking temperature and undersuperatmospheric pressure; separating tar constituents from the productsof conversion thereby obtained and fractionating the products ofconversion to recover cracked gas-oil constituents; subjecting virginand cracked gas-oil constituents recovered as aforesaid to conversion ata relatively low pressure in the presence of a catalyst capable ofpromoting pyrolysis reactions, and separately fractionating theresultant products of conversion to recover gasoline andheavierconstituents therefrom; subjecting said naphtha fraction to thermalconversion at a high cracking temperature and under a relatively highsuperatmospheric pressure, effective to cause the formation ofgasoline-like products having an increased anti-knock value, andfractionating the resultant products of conversion to recover gasolineand heavier constituents therefrom; recovering normally gaseoushydr'ocarbons having 3 to 4 carbon atoms per molecule from the gaseousproducts leaving the several cracking operationsreferred to above; andsubjecting portions of said normally gaseous hydrocarbons to conversionin admixture with the residual fraction and the naphtha fractionsubjected to conversion as aforesaid, respectively.

HORACE B. COOKE.

OERTEEICATE OE CORRECTION. Patent No. 2,558,1LL9. september 12, 19ML.

HORACE B. COOKE,

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 8,sec- 0nd Column, line 20, claim 6, for the Claim reference numeral "18"read -5; and that the said Letters Patent should be read with thiscorrection therein that the same may conform to the record of the Oasein the Patent Office. C I

Signed. and sealed this llth day of November, A. D. 19ML.

Leslie Fraz-er (Seal) Acting; Commissioner of Patents.

